Sintered porous frame and its producing method

ABSTRACT

A structure and construction method of sintered porous frame. The structure of present invention can be applied as a soot filter and catalyst converter to treat exhaust gas from internal combustion engines by coating a layer of catalyst material such as platinum. The inventor use the combustible material foam as a porous substrate to coat a metallic layer. Further the procedure is to apply a sintering process to form a sintered porous frame. Thus the user can use the sintered porous frame to proceed catalyst coating or photo-catalyst coating.

RELATED APPLICATIONS

This application is a Divisional patent application of co-pendingapplication Ser. No. 10/914,246, filed on 10 Aug. 2004.

BACKGROUND OF THE INVENTION

1. Field of The Invention Present invention relates to a structure andconstruction method of sintered porous frame. The structure of presentinvention can be applied as a soot filter and catalyst converter totreat exhaust gas from internal combustion engines by coating a layer ofcatalyst material such as platinum. Also the sintered porous frame canbe applied as an air-cleaning filter to be applied in the air ventingsystem by coating a layer of anti-microbe material such as photocatalyst.

2. Description of the Related

A metallic honeycomb body has passages through which exhaust gas canpass from one end to the other. The honeycomb is obtained from a flatmetal sheet and corrugated metal sheet, and which are welded together.The combined sheet is rolled and coated with desired catalysts, and thenwrapped with a metal case to form a catalyst converter. Detailedproduction process is described in U.S. Pat. No. 5,306,890.

The above prior art can only provide the primary structure with theability to establish a large surface area to enhance the effect ofcatalyst in the exhausting pipe of a combustion engine. But the skill isconstrained on the welding process being high cost for working. Also thesurface area is constrained on the skill level of metal working.

Some methods to improve the structure of the above skill include, U.S.Pat. No. 5,481,084 describes a method to treat metal sheet surface withelectric arc to increase surface area. U.S. Pat. No. 5,567,395 describesa method to provide a turbulence generating section within the honeycombto improve efficiency. U.S. Pat. No. 6,036,926 & WO9715393 describes amethod to use bent-over re-enforced metal sheet to produce a honeycombwith reinforced structure and to improve efficiency. The contactsurfaces from above are still within a limited improvement. Because thesurface-extra structure usually suffers from insufficient adhesion tothe metal surface and has adhesion durability problem after severalthermal shock cycle.

Owing to its coarse passages, the honeycomb can not be used to filtersoot (particles) from diesel engine exhaust. An extra, finer filter (orcalled “soot trap”) is usually required to be installed either beforethe honeycomb converter (U.S. Pat. No. 4,719,571), or parallel to theconverter and control exhaust flow pass through selected chambermechanically, to capture the soot (U.S. Pat. No. 5,264,186). It canprevent the poisoning of catalyst by such soot, and reduce sootemission. However, it is a complicate process and need to install anextra filter unit, which increase cost and weight for a vehicle.

Converter will be heated up while engine starts, and quenched while theengine stops. The repeated cycle usually causes thermal shock to theconverter structure. There are methods to improve its strength byspecial welding (U.S. Pat. No. 5,316,997), or to provide a buffer zoneto accommodate metal thermal- expansion mechanically (U.S. Pat. No.5,403,558, U.S. Pat. No. 6,467,169, U.S. Pat. No. 6,458,329, U.S. Pat.No. 5,846,495). However, such buffer section will require extra spacefor thermal expansion need, which either reduce usable surface area, orincrease total volume of the converter. If the diameter of the converteris increased then there will be a problem to have exhaust gas passesthrough evenly through all the passages. If the length of the converteris increased, then, there will be an increase of back-pressure to theengine.

80% of current air pollutant is from the emission while engine &converter has not yet reached its working temperature. Therefore, thereare methods to provide a solution, e.g. zeolite or molecular sieveabsorbent chamber (U.S. Pat. No. 5,051,244, U.S. Pat. No. 5,108,716) ora separate preheating device (U.S. Pat. No. 5,296,198, U.S. Pat. No.5,465,573, etc.) are described. However, such device either increaseback pressure or reduce fuel efficiency.

Ceramic is strong in compression, and can be coated with catalyst andwrapped with a metal case for catalyst converter application. A detaildescription of the process can be found in U.S. Pat. No. 4,556,543.Ceramic honeycomb with 400 channels per square inch can be produced fromeither extrusion or extrusion molded (U.S. Pat. No. 6,680,101).

Ceramic is strong with compression, but however, has only poor thermalshock resistance. It can be cracked with limit cycle ofheating/quenching, which leads to performance loss. There are methods toreinforce the thermal shock resistance by applying thicker walls tocertain channels (US 2004/0101654), or trying to improve the thermalshock problem with specified L/D of the converter (US) or specifiedshape (semi-oval) of the converter (U.S. Pat. No. 5,304,351). But suchmethods can not satisfy the need for a light-weight, effective catalystcarrier.

Due to the heat capacity and low thermal conductivity of ceramic, theceramic honeycomb takes longer time to reach its operational temperatureafter engine starts. As already describe in metal honeycomb, such lowperformance has create problem and need extra filter or anotherpre-heater to treat the exhaust gas while engine/converter are stillbelow its operation temperature. It increases cost and weight, hencereduce fuel efficiency for a vehicle.

A ceramic foam structure as described in U.S. Pat. No. 4,451,441includes the use of a fine cell (15 to 50 ppi, pores per inch) ceramicfoam as filter, and a coarse cell (2 to 20 ppi) as catalyst carrier forcatalyst converter system. It is claimed to provide a light weight, highsurface area, and much less back-pressure solution for catalystapplication. The ceramic foam is produced by coating a reticulatedpolyurethane foam with ceramic slurry and then sintered it in about750.degree. C. to form a ceramic foam. Polyurethane polymer is in fact,bum-out in the sintering. However, due to the weak mechanical strengthof such tiny ceramic foam strut, it can not satisfy the need to passthermal shock and provide sufficient strength, during service life.

U.S. Pat. No. 5,422,085 describes a method to reduce nitrogen oxide(NOx) emissions in diesel engine exhaust gases. The NOx laden stream istreated with a silver catalyst supported on a nickel coated foam, whichis made by chemical coating of nickel on a polyurethane foam substrate.Owing to the high activity of silver with sulfide in an internalcombustion engine exhaust atmosphere, and the insufficient corrosion-and oxidation resistance of nickel in oxidizing atmosphere, this devicehas not been actually produced commercially.

The ceramic structure is still with a new requirement on manufacturingand transportation. The manufacturing process for ceramic honeycombrequires precise tooling for molding. Also the tooling has its lifecycle and maintenance duty. Also the ceramic material needs godprotection on transportation to prevention impact damage. Thus theproduction cost is high and new structure for catalyst converter isstill required.

Present invention provides a convenience structure and constructionmethod on a low production cost to meet the many requirements. Presentinvention inherits traditional advantages can provide property on largearea for catalyst efficiency, efficient to filter diesel soot(particle), thermal shock resistance and short warm-up time.

SUMMARY OF THE INVENTION

The major purpose of present invention is to provide a structure andconstruction method on sintered porous frame to handle massiveproduction in low cost and high quality which can be used on gasexhausting of a vehicle or the air venting system for air cleaning.

To achieve the above purpose, the core structure of present invention isstill similar to the traditional porous structure of the prior art. Theinventor use the combustible material foam as a porous substrate to coata metallic layer. Further the procedure is to apply a sintering processto form a sintered porous frame. Thus the user can use the sinteredporous frame to proceed catalyst coating or photo-catalyst coating.

The structure of the present invention comprises a porous structure withmetallic-bond or covalent bond inside the structure to connect thewhole-body, and the material of the porous structure have the bearingability for a sintering process with certain temperature range; whereinthe material of porous structure is at least half part formed bymetallic material.

The method of the present invention comprises the following steps: toget the porous substrate by a kind of combustible material; to proceedthe coating process by a metallic material being able to bearing thecombustion temperature of the combustible material; to put the coatedporous substrate into sintering process to remove the combustiblesubstrate and to generate the porous structure by metallic materialthrough metallic-bond or covalent bond inside the structure to connectthe whole-body to produce the sintered porous frame.

Drawings and the tables only form a part of present specificationwithout any restrictions to present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects and advantages of the present invention will be morereadily understood from the following detailed description when read inconjunction with the appended drawing, in which:

FIG. 1 is a flow-chart diagram of current manufacturing method ofsintered porous frame; and

FIG. 2 is a shape of the cave inside the sintered porous frame.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

What is invented is a method to produce a metallic foam with hightensile strength, high surface area with low back-pressure, low thermalexpansion coefficient, high thermal shock resistance, low weight, anddesign flexibility to provide a proactively heating metallic foam toreduce complexity and improve fuel economic to satisfy the need incatalyst converter application, and at the same time, increase surfacearea to provide a more effective exhaust gas treatment while reducingconverter weight.

Polyurethane foam materials (or similar polymer structure) are firsttreated by electrochemical deposition. For ensuring theelectro-conductivity, copper sulfide electroconductive (94 wt % ofcopper sulfide and 6 wt % of epoxy binder) layer is precoated on thesurface of the polyurethane foam. There are other electroconductivelayers, e.g. graphite, carbon black, etc., can also be used. There areother methods to provide an electroconductive layer on the polyurethanesubstrate, like PVD, CVD, chemical plating, etc. The resultedpolyurethane foam material is then plated electrically with any desiredmetal, or a special metal composition. The later can be achieved byadjusting electrode and plating bath composition. After the electricalplating with a certain thickness (usually from 60 to 150 microns) ofmetal on top of the polyurethane foam and electroconductive layer, theresulted foam is then sintered in a hydrogen-ammonia atmosphere at350.degree. C. to 500.degree. C. for 30.about.45 minutes in a furnace,and then the temperature is increased to 650.degree. C. to 900.degree.C. gradually in about 30 minutes. The foam is reducible in the furnaceof 650.degree. C. to 900.degree. C. with hydrogen-ammonia atmosphere foranother 60.about.90 minutes. The sintering temperature need to becontrolled carefully in order not to melt the metal composition, butneed to allow the metal compositions to be reduced.

Polyurethane polymer within the foam material is then bum-out, leaving ahollow triangular cave (maybe other kind of cave shape), covered by themetal. Please also refer to the FIG. 2 The cave can reduce the thermalexpansion of the whole structure.

The resulted metallic foam can then be coated with catalyst compositionfrom previous coating technologies for catalyst converter applications.The resulted foam is an ideal carrier body not only can be used as acarrier for such catalysts, but a foam with finer cell structure (90 to120 ppi) also can be used as a diesel soot trap (or called “filter). Thecell structure is only limited by the original polyurethane foammorphology. Therefore, a cell size from 5 to 150 ppi can be produced.

The hollow cave under the metal strut can provide the metallic foam withexcellent strength and thermal shock resistance. Owing to the shape ofthe metal walls, the linear thermal expansion of such foam is very low,which provides good dimensional and thermal shock stability. The hollowcave also provides a maximum surface area with less material weight. Thereduced weight requires less heat to warm-up the foam, hence a convertermade from the foam can be heated-up to operational temperature faster.

Another benefit from this invention is the metallic foam can be coatedwith a nickel-chromium alloy on the out surface. It can then be heatedwith adequate electric current from an automobile electricity generatoror batterer. It provide a proactively heating carrier, which can be usedto replaced any carrier material described in prior art for bothcatalyst converter or filter/trap. It simplify current requirement tohave dual chambers, and reduce manufacturing cost with fuel efficiencyimprovement.

FIG. 1 is the flow-chart diagram of current manufacturing method ofsintered porous frame. The sintered porous frame can be widely used inthe fluid transferring machine for some treatment of chemical reaction.The manufacturing method comprises: to get the porous substrate by akind of combustible material (such as the polymer foam); to proceed thecoating process by a metallic material being able to bearing thecombustion temperature of the combustible material; to put the coatedporous substrate into sintering process to remove the combustiblesubstrate and to generate the porous structure by metallic materialthrough metallic-bond or covalent bond inside the structure to connectthe whole-body to produce the sintered porous frame. Wherein themetallic bond is easy to be recognized as common bond in the metal oralloy and the covalent bond is for the little non-metal material insidethe metal base generated form sintering or for property improvement ofmetal base.

The steps of the present invention also contains the below variations:Wherein the coating process can contains two sub-processes for ease toattach the metal material on the combustible material, the pre-coatingprocess and the enhanced-coating process, the pre-coating process forbinding a layer of metal-plating-allowable material on the poroussubstrate, the enhanced-coating process for plating a thick layer ofmetallic material to construct the main porous structure of the sinteredporous frame. Wherein the pre-coating process can be to sputter metal ormetal-plating-allowable material on the porous substrate. Wherein thepre-coating process can be to spread the conductive glue on the poroussubstrate. Wherein the spreading method for conductive glue is byspraying. Wherein the pre-coating process can be to put the poroussubstrate into the specified chemical solution, the specified chemicalsolution being contained the metal-plating-allowable material. Whereinthe metallic material comprise nickel or chromium to have the ability toheat the porous structure with electrical power for industrialapplication. (such as pre heating in the exhausting pipe of the vehicle)Wherein the metallic material comprises copper, aluminum or their alloythat the metal can have the flexibility for installation and heatdurability in sintering process.

Wherein the sintering process can contain the process to generate themetal deoxidation in the gas contained ammonia.

The structure of the sintered porous frame comprises: a porous structurewith metallic-bond or covalent bond inside the structure to connect thewhole-body, and the material of the porous structure have the bearingability for a sintering process with certain temperature range; whereinthe material of porous structure is at least 90 percent to whole bodyformed by metallic material.

The variations of the structure of the sintered porous frame aredescribed in the bellow: Wherein the porous structure has little holesinside and the wall of little hole have the residual carbon compoundgenerated by the heating process of sintering. Wherein the porousstructure can be bended allowable to form a special shape to fit thepredetermined space in the flowing-fluid device. (such as ventilationpipe or gas exhausting pipe) Wherein the certain temperature range canbe from 150-900 Centigrade. Wherein the porous structure can be coatedwith a catalyst material or anti-microbe material. Wherein the metallicmaterial can comprise copper, aluminum or their alloy. Wherein themetallic material can comprise nickel or chromium to have the ability toheat the porous structure with electrical power for industrialapplication.

The present invention can provide many benefits then the prior art. Suchas the no-welding point structure, high catalyst efficiency from nonuniform porous structure, efficient to filter diesel soot (particle),thermal shock resistance and short warm-up time. Also the cost isreasonable for mass production.

In addition the structure of the present invention can be applied as abase frame to coat the material of photo catalyst because of theproperty of the sintered porous frame having the above described manybenefits. Nearly 40 years after the publication of the photo-catalysttheory on 1972 Nature magazine, TiO2 has only been studying in recentlytwo decades under the environmental protection against pollution.Previously, the photo-TiO2-catalyst only works under ultraviolet,nowadays, practical TiO2 products work under visible light come into themarket in succession.

Also the application area of the sintered porous frame can be extendedto the chemical engineering industry for example to coat a layer ofcatalyst for function of De-NOx or De-SOx.

Above is the optimal implementation of present invention, it will beapparent that various changes and modifications can be made withoutdeparting from the scope of the invention as defined in the claims.

1. A method to produce the sintered porous frame comprising thefollowing steps: providing a porous substrate by a kind of combustiblematerial; proceeding a coating process by a metallic material being ableto bearing the combustion temperature of the combustible material; andputting a coated porous substrate into sintering process to remove thecombustible substrate and to generate the porous structure by metallicmaterial through metallic-bond or covalent bond inside the structure toconnect the whole-body to produce the sintered porous frame.
 2. Themethod to produce the sintered porous frame as claimed in claim 1,wherein the coating process contains two sub-processes, the pre-coatingprocess and the enhanced-coating process, the pre-coating process forbinding a layer of metal-plating-allowable material on the poroussubstrate, the enhanced-coating process for plating a thick layer ofmetallic material to construct the main porous structure of the sinteredporous frame.
 3. The method to produce the sintered porous frame asclaimed in claim 2, wherein the pre-coating process is to sputter metalor metal-plating-allowable material on the porous substrate.
 4. Themethod to produce the sintered porous frame as claimed in claim 2,wherein the pre-coating process is to spread the conductive glue on theporous substrate.
 5. The method to produce the sintered porous frame asclaimed in claim 4, wherein the spreading method for conductive glue isby spraying.
 6. The method to produce the sintered porous frame asclaimed in claim 2, wherein the pre-coating process is to put the poroussubstrate into the specified chemical solution, the specified chemicalsolution being contained the metal-plating-allowable material.
 7. Themethod to produce the sintered porous frame as claimed in claim 1,wherein the metallic material comprise nickel or chromium to have theability to heat the porous structure with electrical power forindustrial application.
 8. The method to produce the sintered porousframe as claimed in claim 1, wherein the metallic material comprisescopper, aluminum or their alloy.
 9. The method to produce the sinteredporous frame as claimed in claim 1, wherein the sintering processcontains the process to generate the metal deoxidation in the gascontained ammonia.